U.S. patent number 4,021,338 [Application Number 05/739,979] was granted by the patent office on 1977-05-03 for method for treating septic tank effluent seepage beds and the like.
This patent grant is currently assigned to Wisconsin Alumni Research Foundation. Invention is credited to John M. Harkin.
United States Patent |
4,021,338 |
Harkin |
May 3, 1977 |
Method for treating septic tank effluent seepage beds and the
like
Abstract
A method for correcting and preventing the failure of septic
tank effluent seepage beds or similar installations which comprises
treating such beds with a solution of an oxidizing agent,
preferably hydrogen peroxide.
Inventors: |
Harkin; John M. (Madison,
WI) |
Assignee: |
Wisconsin Alumni Research
Foundation (Madison, WI)
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Family
ID: |
27084238 |
Appl.
No.: |
05/739,979 |
Filed: |
November 8, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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602764 |
Aug 7, 1976 |
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Current U.S.
Class: |
210/747.1;
405/50; 210/759 |
Current CPC
Class: |
C02F
3/046 (20130101); C02F 1/722 (20130101); E03F
1/002 (20130101); Y02W 10/15 (20150501); Y02W
10/10 (20150501) |
Current International
Class: |
C02F
1/72 (20060101); C02F 3/04 (20060101); E03F
1/00 (20060101); E02B 011/00 (); C02B 001/34 ();
C02B 003/08 () |
Field of
Search: |
;210/15,18,50,63R
;61/13 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Proceedings of the 21st Industrial Waste Conference, May 3, 4, and
5, 1966, Purdue University, Lafayette, Indiana, "Hydrogen Sulfide
and Methyl Mercaptan Removals with Soil Columns," pp.
172-191..
|
Primary Examiner: Spear, Jr.; Frank A.
Assistant Examiner: Therkorn; Ernest G.
Attorney, Agent or Firm: Bremer; Howard W.
Parent Case Text
This application is a continuation-in-part of application Ser. No.
602,764, filed Aug. 7, 1975.
Claims
Having thus described the invention what is claimed is:
1. A method for rehabilitating or improving the permeability of a
septic tank effluent seepage bed, which has become at least partly
inoperative because of blocking or clogging of the soil pores in
such bed, which consists of treating said bed with hydrogen
peroxide in an amount sufficient to increase the permeability and
thereby the functionality of said bed.
2. The method of claim 1 wherein the hydrogen peroxide is used at a
concentration of from about 25% to about 65% by weight.
3. A method of treating the clogged or crusted and ponded effluent
seepage bed of a septic system containing in combination a septic
tank with an effluent exit port, and effluent distribution box or
manifold, effluent distribution lines emanating from said box or
manifold and an effluent seepage bed associated with said
distribution lines, which method consists of, pumping said septic
tank to lower the liquid level in said tank substantially below the
effluent exist port, substantially reducing the volume of water
ponded in said seepage bed and treating said seepage bed with
hydrogen peroxide in an amount sufficient to increase the
permeability thereof and thereby its functionality.
Description
This invention relates to an improved method for treating septic
tank effluent seepage beds and like installations.
More particularly, this invention relates to a method for treating
such installations which have failed through clogging, whereby the
seepage or leach bed is "opened up" to again permit purifying
percolation of effluent through the bed.
This invention also relates to a method for prophylactically
treating septic tank effluent beds or the like to prevent failure
through clogging.
Safe and effective management of wastewaters discharged from single
and multiple family dwellings, motels, restaurants, campsites, ski
resorts and similar living units or establishments remote from
central municipal sewerage systems is a major problem in many areas
of the world. Treatment systems involving anaerobic digestion of
the raw wastes in a septic tank followed by disposal of the septic
tank effluent in a soil absorption/purification seepage bed are now
almost exclusively used for on-site disposal of wastewaters in
unsewered areas. Occasionally, other devices, such as aerators,
sand filters, or biological discs, are interspersed between the
tank and the bed to prepurify the tank effluent (e.g. by B.O.D.
reduction or suspended solids removal) before it is admitted to the
seepage bed.
It is well known, however, that simple or adapted septic tank/soil
seepage systems are sometimes ineffective in preventing public
health hazards and nuisances because of the failure of the systems
to function in the intended fashion. Localized septic tank system
failures have sometimes been condoned where they have occured in
rural areas with low population density. With the rapid growth of
high-density suburban, summer-home, and recreational communities in
unsewered areas, however, failure of septic systems cannot be
tolerated because of the public health hazards engendered by
potential surface and drinking water contamination resulting from
such failures.
Household wastewaters are recognized as containing fecal and
occasionally pathogenic bacteria, putrescible organic materials,
high loads of inorganic and organic plant nutrients, particularly
compounds of nitrogen and phosphorus, and, on occasion, infectious
viruses. Household sewage can thus cause serious health and
environmental problems if released to surface or groundwater
without prior purification. In areas remote from large-scale
municipal sewage treatment plants, underground septic tank-soil
seepage bed systems can be used to effect satisfactory
purification, provided the systems are properly designed, installed
and maintained in appropriate soils. In suitable systems the septic
tank prevents the bulk of waste solids suspended in the wastewater
from reaching the soil absorption field and rapidly clogging the
soil pores. In the tank, heavier solids sink to the bottom as a
sludge and are decomposed by anaerobic microorganisms, while grease
and lighter solids form a floating scum. The liquid component of
the wastewaters, clarified by such settling and flotation,
gradually flows from the tank at a point intermediate the sludge
and floating layers and is distributed through a system of
perforated pipes located underground in a series of trenches filled
with gravel, to spread the effluent evenly over a large disposal
area in the soil. This latter disposal area is referred to as a
seepage bed or leach or absorption field. The septic tank effluent
still contains small amounts of suspended solids, dissolved
putrescible solids, bacteria/virus, and soluble plant nutrients. In
a properly functioning seepage bed, the soil pores filter out the
residual suspended solids, bacteria and virus as the liquid drains
or percolates through the soil. At the same time the bulk of the
dissolved organic compounds are decomposed aerobically and/or
anaerobically by soil microorganisms. Phosphates in the effluent
are generally efficiently retained in the soil, e.g. by absorption
on clay particles, while nutrient nitrogenous compounds are
normally oxidized to nitrates, which tend to drain away into the
groundwater or be partially decomposed to elemental nitrogen under
anaerobic conditions by denitrifying bacteria. With the exception
of nitrate, a properly functioning absorption field almost
completely purifies the septic tank effluent before the water
reaches the underground water table or aquifer.
Some soils are unsuitable for septic tank-soil disposal systems.
The rate at which water seeps through the soil (the so-called
percolation rate) may be too slow, or the soil cover (depth) above
highly permeable, creviced bedrock or a high water table may be too
thin, or the slope of the terrain may be too steep, or the site may
be located on a river flood plain subject to seasonal inundation.
In some problem areas soil can be heaped up into a mound to create
an artificial purification bed which allows adequate purification.
In such installations, effluent from the septic tank is pumped up
into a distribution system in the mound, which functions like a
normal subsurface seepage bed in conventional systems.
However, even with well designed systems, properly installed on
suitable soils, failures can and do occur. Such failures are
generally caused by the inability of the soil to conduct away water
from the tank effluent at an adequate rate - a problem which is
greatly enhanced in the modern household through the use of
automatic water-using appliances such as water softeners,
dishwashers and washing machines. As a result, either effluent
surfaces and contaminates the area around the seepage bed, possibly
also polluting surface waters, or the septic tank may overfill with
water and the system may back up inside the house or buildings
being serviced.
The reduction in the rate of water seepage through the soil
purification bed may be due to one or more of several factors,
including: (1.) blockage of capillary pores in the soil by
particles of suspended solids filtered from the septic tank
effluent; (2.) blockage of soil pores by the cells of soil
microoganisms growing on the dissolved and suspended organic matter
present in the effluent; (3.) deposition of microbial metabolites,
especially bacterial polysaccharide slimes and gums, in the seepage
bed; (4.) precipitation of insoluble heavy metal sulfides in
anaerobic portions of the bed; and (5.) gas locks due to nitrogen,
methane or other gases released in the bed. These contributing
factors, in combination or progression, can cause failure of the
system.
Before a septic system is installed, soil surveys are generally
made to determine whether the site is amenable to such systems and
a percolation test is run to determine whether the soil will permit
liquid to move out of bed of reasonable dimensions at a rate
commensurate with projected needs. When a newly installed system
begins to operate, the tank effluent will usually drain away
rapidly from the seepage bed while efficient purification takes
place through the filtering action of the soil, decomposition of
the organic contaminants by aerobic soil microoganisms, and
fixation of plant nutrient elements by adsorption processes and
conversion to microbial biomass in the bed. As filtration of
intractable organic solids and proliferation of bacterial cells
proceeds in the bed, a gradual initial blocking of the soil
capillaries occurs, so that the system does not drain as fast as it
did in its virgin condition. As a result, air cannot be drawn into
the soil in a quantity sufficient to maintain an adequate rate of
aerobic decomposition of incoming organic materials. Such air is
the only source of oxygen in the bed, there being no dissolved
oxygen in the septic tank effluent since it has emerged from a
completely anaerobic fermentation zone. Consequently, continuously
ponded anaerobic zones tend to develop in the seepage bed. Some
decomposition of organic matter by anaerobic microorganisms still
goes in these zones, but layers resistant to flow begin to develop
in the bed as fresh suspended organic materials from inflowing tank
effluent are deposited in the bed, microbial cells proliferate, and
excretion of solid microbial metabolites continues, to the point
where these actions predominate and ultimately cause formation of
impenetrable crusts or clogged zones. The anaerobic conditions
particularly promote the formation of bacterial slimes and gums and
the reduction of sulfates in the effluent to sulfide, with the
result that black insoluble heavy metal sulfides precipitate in the
blocked, clogged, or crusted zones. The extent of such blackened
regions depends upon the hydraulic head on the bed and on the
length of time over which the anaerobic condition has prevailed.
The formation of sulfides also interferes with microbial conversion
of wastes in the bed since sulfides are toxic to many species of
microoganisms. Also, precipitation of insoluble sulfides may tie up
in unavailable form some trace elements, such as iron, manganese,
or copper, needed by some soil microbes for the synthesis of
enzymes essential to maintain normal growth and metabolism.
For many decades, and perhaps as long as reasonably modern septic
systems have been available, all sorts of nostrums have been
suggested to combat or cure system failure. For the most part these
nostrums have consisted of strong bases, strong acids, detergents,
surfactants, bacterial inocula, yeast inocula, fungi inocula and
enzymes. The Government's "Manual of Septic Tank Practice" teaches
that thousands of such nostrums have been marketed. None of these
has, however, proved to be efficacious in "opening up" a clogged
septic tank leach field. The Manual consequently warns against the
use of such materials since they often compound rather than
alleviate the problems of soil clogging and system failure.
Prior to the present invention, possibly the most reliable remedy
one could prescribe in an attempt to cure a failed system is to
stop using it. Sometimes the short rest that can be achieved by
pumping out the contents of the septic tank will help revive a
failed system since it generally takes a few days before a properly
dimensioned tank refills and during this time, ponded water may
slowly seep away through small unclogged portions of the bed,
readmitting air to the anaerobic clogged zones. As air reenters
these regions, the anaerobic organisms are killed off, because they
cannot tolerate oxygen. The chemical species formed during this
process, the oxygen ion or superoxide radical (see I. Fridovich,
Accounts of Chemical Research, 5 (10) --321-326 (1972)) reoxidizes
a portion of the black sulfides to sulfates, causing some
brightening of the dark zones, and aerobic bacterial decomposition
of the wastes clogging the bed may be stimulated. (See P. H.
McGauhey, R. B. Krone, Soil Mantle As A Waste Water Treatment
System, SERL Report No. 67-11, University of California Berkeley,
1967.)
However, unless the resting period is long enough, the bed is not
adequately reaerated to rehabilitate it. In practice, the amount of
insoluble sulfide that is oxidized on resting the bed is limited
since there are only sufficient anaerobes in the bed to form only
limited amounts of superoxide radical. Also, to permit air to be
admitted to the bed water must drain from it during resting, the
subsequent moisture regime in the soil may not be optimum for
decomposition of residual organics by aerobic organisms. Therefore,
development of anaerobic conditions and clogged/crusted layers in
the bed recurs very rapidly when the system is returned to
operation and recurring failure due to clogging/crusting following
resting of a bed takes place much faster than with a freshly
constructed bed. Also, in practice, it is usually impractical to
interrupt the use of a septic system for long enough to provide a
satisfactory resting period in order to allow rejuvenation or
recovery of a failed seepage bed.
It has now been found that failed septic tank seepage beds can be
again made functional by treating them with certain chemical
oxidizing agents. Such treatment can also be effectively applied to
similar wastewater treatment systems, such as dry wells, sand
filters, or sand or soil beds used for treatment of sewage or
effluents.
Theoretically, any chemical oxidizing agent, whether in solid,
liquid or gaseous form could be used for the purposes of this
invention. However, many have been found to be inoperative for such
purposes and the use of others is militated against because of
practical considerations.
For example, U.S. Pat. No. 2,768,949 discloses a method for
treating clogged underground sewage drain systems utilizing a
decomposing acid (sulfuric acid or phosphoric acid) to solubilize
clogging material and optionally enhanced by an ammonia reagent
(ammonium hydroxide) or a strong oxidizing agent such as potassium
permanganate. All of these chemicals are applied in accordance with
the teachings of this patent by drilling holes (as preferably by
hydraulic nozzle means) into the clogged formation and filling the
chemicals into the holes. Physical break-up of the clogging
materials by such hydraulic nozzles is also advocated.
It is clear from the disclosure of U.S. Pat. No. 2,768,949 that it
contemplates "so treating the accumulated clogging material within
the chamber and formation as to disintegrate and decompose it - - -
". Inasmuch as the primary treating agents are strong acids,
sulfuric and phosphoric, the obvious intent is to dissolve the
clogging materials by acid-catalyzed chemical reaction. As a matter
of fact, only a small fraction of the clogging materials can be
dissolved by such acids since many of the organic compounds present
in clogged solid are not prone to acidic hydrolysis. Moreover,
strong mineral acids, such as sulfuric, phosphoric and nitric acid,
particularly when applied in undiluted form, drastically alter the
pH of the soil, making it unsuitable to support growth of the
heterotrophic bacteria that normally destroy the organic wastes and
fix the inorganic nutrients present in septic tank effluent. In
effect, they would destroy the natural condition of the soil and
render it ineffective as a medium for biological purification and
renovation of waste waters. They are, therefore, environmentally
unacceptable.
In addition, and regardless of dilution, sulfuric and phosphoric
acid would liberate hydrogen sulfide in free gaseous form from the
copious deposits of insoluble metal sulfides present in the clogged
soil -- a gas which is not only toxic to humans and other higher
life forms but also to soil microorganisms and would, therefore,
further reduce the biological activity in the soil surrounding the
acid-treated systems.
It should also not be overlooked that the strong mineral acids
would react vigorously with carbonates in calcareous soils as well
as with crushed limestone which is frequently used as the gravel
medium in leach field beds -- reactions which could not only be
deleterious but even hazardous -- and that excess acid could be
leached from the soil and adversely effect ground water quality.
Phosphoric acid presents the additional complication of the
potential formation of gelatinous precipitates of certain
phosphates, e.g. calcium or iron phosphate, which might increase
rather than decrease the clogging in the treated soil, while nitric
acid poses the danger of ground water contamination with
nitrates.
The use of a strong oxidizing agent, such as potassium
permanganate, as an adjunct to the acid treatment, as suggested in
U.S. Pat. No. 2,768,949, will not alleviate or offset the
deleterious effects of the primary strong mineral acid treatment
and, as a practical matter, are too expensive to use.
None of the acidic reagents taught by U.S. Pat. No. 2,768,949 leave
the soil in a fit condition for the desired natural
physical-biological purification of waste waters by a vigorous
mixed soil bacterial population.
Certain other well-known oxidizing agents suggest themselves for
purposes of this invention but as a practical matter are
unsuitable. For example, chlorine and oxychlorides would appear to
be readily usable in solution form. However, such agents are highly
toxic to microoganisms and would also tend to chlorinate the
organic matter in the seepage bed, creating chlorinated organic
compounds which are more resistant to biological degradation, or,
perhaps, chloramines, which are highly toxic and assumed to be
carcinogenic.
Still other inorganic or organic peroxides, such as sodium
peroxide, t-butyl hydroperoxide, or peroxyacetic acid could also
conceivably be used for the purposes of this invention. These
would, however, not be preferred compounds because of the
possibility of creating undesirable pH changes in the seepage bed
and because of cost considerations.
In particular contrast to the acid treatment prescribed in U.S.
Pat. No. 2,768,949, the process of the present invention, a simple
treatment with hydrogen peroxide, is designed to stimulate the
natural biological breakdown of clogging substances with minor
chemical action while the treating agent decomposes into
environmentally harmless components. Presumably gaseous oxygen or
ozone could be used in the process of the present invention instead
of hydrogen peroxide. These agents are, obviously difficult to
inject into and distribute through the soil bed and are therefore
not practical alternatives to the treating agent of choice,
hydrogen peroxide.
When applied to a clogged seepage bed in accordance with this
invention, hydrogen peroxide oxidizes the bulk of the insoluble
sulfides present in the clogged and crusted bed to harmless sulfur,
soluble sulfates, and other oxysulfur anions, thereby destroying
the toxic sulfides and releasing the heavy metal trace elements to
the soil solution for microbial use. Some of the peroxide may
decompose to water plus oxygen, either catalytically on soil
particles or by heavy metal ions brought into solution by the
oxidation of insoluble sulfides, or through enzymatic decomposition
by catalases produced by organisms present in the bed. The freed
oxygen causes considerable turbulence in the bed, which loosens up
the soil particles and pores, especially in the organically matted
clogged areas, and mechanically improves the distribution of the
chemical throughout the bed and the permeability of the soil. The
free oxygen can also be reduced in part to oxygen radical anions by
the anaerobic bacteria in the bed, and so its efficacy is
multiplied. Some direct chemical oxidation of the clogging organic
matter by peroxide, oxygen, or oxygen ion radicals may also occur,
promoting destruction or solubilization of these obstructing
compounds, e.g. by introduction of polar oxygen functions such as
carboxylic acid groupings. Biological decomposition of the organic
materials in the bed by aerobic organisms is also stimulated. The
combination of these effects rapidly restores permeability to
clogged and crusted regions of the bed, returning the bed to the
status of intermittent drainage typical of a freshly constructed
bed.
The hydrogen peroxide treatment can be carried out in various ways,
depending upon the condition of the system being treated but to be
fully effective the peroxide should reach the clogged, crusted
anaerobic portions of the bed. The efficacy of the treatment is
therefore reduced both by dilution and by inaccessibility of target
areas if the peroxide is added to a bed which is standing full of
water, such as is present in many failed systems. Preferably this
water should be pumped out, and disposed of safely, and replaced by
peroxide solution. The peroxide is thus given the opportunity to
reach the areas which are sealed and which were supporting the
water being held in the bed. Alternatively, the septic tank can be
pumped out, allowing a few days' respite to the bed. During this
time, the bed may drain sufficiently by natural percolation. The
emptied tank can also be used as a temporary or intermediate
holding facility for water subsequently removed from the bed. After
the bed has been drained, peroxide is added to the bed either
immediately or shortly before fresh effluent begins to spill over
again from the tank. A combination of bed and tank pumping can also
be carried out.
Prevention of failure is, of course, preferable to correcting
failure. Thus, as another embodiment of this invention, peroxide
treatment can be used to forestall failure of the system. Such
prophylactic treatment can be readily performed as part of routine
service or maintenance of the septic system. Septic tanks must be
pumped out occasionally to remove the solid sludge that gradually
accumulates on the bottom of the tank, otherwise large charges of
solids spill over into the distribution pipes and disposal bed and
cause rapid clogging of the whole system. According to the present
invention, when practiced for prophylactic purposes, whenever a
tank is pumped out, the bed should be allowed to drain naturally
for the few days, until the liquid in the tank has almost reached
the effluent exit port, and hydrogen peroxide then added to the bed
to rejuvenate the bed by removing any crusts that have been
building up. This prophylactic treatment can restore the
permeability of the bed to its virginal condition. Alternatively,
hydrogen peroxide can be added to the bed while the tank is being
pumped out or any time after it has been emptied.
The peroxide can be introduced into the system by any of a variety
of methods. It can be injected at one point or at several spots
distributed throughout the bed using probes similar to oversize
injection needles. It is much simpler to pump, pour or siphon a
hydrogen peroxide solution down the vent pipes normally located at
the ends of distribution lines or into the distribution box or
manifold located at the start of the distribution system. Special
pipes can also be provided in beds to serve as a distributing line
for hydrogen peroxide treatments. Alternatively, holes can be
augered down through the backfill to the top of the gravel and
temporary pipes, e.g. 3" plastic pipe, inserted for introducing the
peroxide to one or several areas along the bed.
The amount and concentration of peroxide needed is highly variable
depending upon the size and state of the system being treated. Any
grade of peroxide is suitable, but stabilized technical grades are
normally preferable. The concentration of the stock solution used
is determined merely by convenience in shipping and handling.
Normally a 30-65% concentration is convenient for use. The stock
solution can be appropriately diluted with water before, during or
after application to the bed. In any event, excess hydrogen
peroxide is not harmful to the soil organisms - it merely
decomposes, either catalytically on soil particles on enzymatically
by microbial catalases, giving water and oxygen which promotes
aerobic decomposition of organic matter in the soil bed.
It has been found that for prophylactic treatments of bed
characteristic to single family living units, 1-5 gallons of
approximately 50% hydrogen peroxide solution is usually adequate
while for treatment of such a system that has failed, i.e. a system
that has become completely sealed by the clogging/crusting
phenomenon, 15-30 gallons of 50% hydrogen peroxide solution is
normally sufficient. Larger or smaller amounts may be required for
other systems, depending on their size, the extent and severity of
the clogged zones, and the length of time for which the system has
been clogged. The volumes and concentrations specified above and in
the following Examples should not be considered, therefore, to
constitute any limitation of the present invention. Any volume or
any concentration of hydrogen peroxide or other peroxidic oxidizing
agent added to a septic tank effluent or other wastewater disposal
system for purposes of avoiding clogging and crusting of the soil
or sand present in the treatment system, or for remedial treatment
of systems that have failed because of crusting, clogging or
sealing of the soil seepage bed is to be considered an embodiment
of the present invention. The extent, duration and mode of the
treatment by the oxidizing agent can be readily adjusted to the
requirements in a given situation.
EXAMPLE 1
A series of polyvinyl chloride columns 75 cm long and 10 cm in
inner diameter were capped at their lower ends. A short half-inch
diameter tube fitted with a stopcock was sealed into each cap. The
top of each column was fitted with a threaded collar into which a
cap fitted with a short plastic nipple could be screwed.
Each column was filled with 60 cm of coarse sandy soil, the upper
surface of the sand being covered with coarse gravel or a glass
wool mat to prevent agitation of the surface particles when liquid
was added to the tubes. The caps were screwed on, using teflon tape
to ensure a good seal, and connected to a reservoir via a tubing
manifold. The soil columns were used to simulate cross-sections or
cores of a septic tank effluent disposal field on a highly porous
soil or a mound system with sandy fill. Septic tank effluent from a
conventional treatment facility was intercepted before entering a
conventional disposal field and trapped in an underground holding
tank, from which liquid was removed weekly by pumping into 5 gallon
containers, which were brought back to the laboratory and stored at
5.degree. C. in a cold room or refrigerated chest. Charges of
effluent (1.7 gallons) were added daily to each column under a
hydrostatic head of 5-80 cm of liquid. The columns were kept
constantly ponded by opening the stopcocks only while additions
were being made and closing them before all the liquid drained from
the top of the column. This procedure maintained the columns in a
continuously anaerobic condition, simulating conditions in a
seepage bed which is beginning to fail because of retarded
percolation. In time, the flow rates of liquid through each column
with the stopcock fully open became gradually slower until after
90-100 days flow with the stopcock open finally ceased or had
fallen to a few milliliters of liquid per hour, even under the
highest hydrostatic heads. This was due to clogging of the soil
pores in the column. A 30% aqueous solution of hydrogen peroxide
was then poured in 50 milliliter increments into the ponded liquid
on top of test columns, until totals of 50, 150, and 250 ml had
been added. Other columns remained untreated as controls.
Unclogging by the peroxide generally resulted within a few hours.
As the treated columns unclogged, the flow rates increased to 450
to 3000 ml per hour under only 10 cm hydrostatic head.
The initial effluents from the unclogged columns were green-blue in
color and contained oxysulfur salts of iron, manganese, nickel,
copper, magnesium, and other cations. The total organic carbon
content of the glass wool covers (8-15% C. in control columns) and
in the upper (0-1, 1-2, and 2-3 cm depth) soil layers (0.50-0.85%
in control columns) were reduced to about half of these values
after flushing with the normal daily dose of effluent following
peroxide treatment. The slimy appearance and feel of coatings on
the gravel and on the uppermost crusted surface of the sandy soil
disappeared. High percolation rates were restored in both sealed
and seriously clogged columns.
EXAMPLE 2
A battery of plexiglass columns 90 cm long and 10 cm in internal
diameter were sealed at the lower end with coverplates fitted with
plastic nipples and tygon tubing equipped with pinchcocks at the
botton end and provided with snugly fitting, but removable nippled
covers at the tops. Each column was filled with 75 cm of medium
grained sand covered with 10 cm of coarse gravel, to simulate cores
through a conventional septic tank effluent seepage bed or mound
fill system. Daily doses of 0.15-1.7 gallons of effluent were added
to each column as described above. A black layer started to form at
the top surface of the sand within a few days. Blackening proceeded
down the whole length of the columns as daily dosing was continued,
while the blackening at the top layers increased in intensity. In
time, the flow rates through the columns with the pinchcocks open
were dramatically decreased or reduced to zero, that is, the soil
pores in the columns were badly clogged or completely sealed. There
was an intensely black crust at the top surface of the sand in each
column. When 50 ml of 30% hydrogen peroxide was added to ponded
effluent at the top of sealed columns, the reagent began to
brighten the black color and to erode into the clogged/crusted
surface. Effervescence and frothing mechanically churned up the
surface layers. In time the reagent gradually ate its way down into
lower layers of the column. If the reagent seemed expended, a
further addition of 50 ml of 30% H.sub.2 O.sub.2 was made. Within a
few hours, breakthrough was achieved, even in sealed columns, and
effluent began to flow again. As before, the first liquid to emerge
from the columns was green-blue and contained inter alia sulfates
of Fe, Mn, Ni, Cu, Mg, etc. Final flow rates of 0.5-3.0 liters per
hour were achieved with 50-250 ml of 30% H.sub.2 O.sub.2 within
3-14 hours. When the gravel covering some columns was carefully
removed and hydrogen peroxide was injected through a long syringe
needle into lower layers of the sand in some test columns, almost
instant brightening of the color occurred, due to the rapid
chemical oxidation of black insoluble transition metal sulfides to
their colorless or only lightly colored, soluble sulfates (or other
oxysulfur salts). The levels of insoluble sulfides are much lower
at deeper levels in the column than at the upper crusts, so that
brightening proceeds much faster. When peroxide was injected into
subsurface portions of the column, some of it started to decompose
catalytically in the columns. The oxygen released bubbled to the
surface, causing agitation of the soil and ruptions in the surface
layer, stirring up the surface and creating channels that
accelerated spread of the reagent and flow of effluent through the
soil. However, both methods of treatment (simple addition or
injection) removed the clogged/crusted condition of the columns and
restored fast percolation rates.
The foregoing example suggests that there could be advantages in
injecting peroxide directly into the seepage bed soil. As a
practical matter this is difficult in field installations because
of the gravel backfill covering the soil. However, well-drilling
probes (sand points) or similar stiff, small-diameter hollow pipes
can be used to penetrate the gravel layer and inject peroxide
directly into the crusted/clogged portions of the bed.
EXAMPLE 3
A seepage field belonging to a household septic system was treated
as described below. This system had failed to the point that the
whole underground disposal field was apparently completely or
almost completely sealed as evidenced by the fact that whenever
water was used in the house, septic tank effluent fountained out of
a vent pipe above the distribution box and ran downhill onto an
adjoining alfalfa field. The disposal field was installed in
glacial till, a soil type which exhibits very high percolation
rates. Failure of the system was therefore undoubtedly due to the
biological clogging/crusting phenomenon. A pit (ca. 5 .times. 4
feet) was carefully dug alongside the seepage bed close to the
distribution box to a depth below the bottom of the ponded water. A
small hole was then burrowed laterally underneath the bed. A soil
moisture tensiometer was inserted into this hole underneath the
bed, and the pit was refilled. Three other vertical holes were made
with a post hole digger laterally along the bed and 10-foot plastic
standpipes were inserted to help view the level of the water in the
bed. At each insertion point, water was found to be standing in the
bed just a few inches below the soil surface. The contents of the
septic tank were pumped out and removed by a commercial serviceman,
and as much as possible of the effluent which had ponded in the bed
was pumped out onto the alfalfa field using a self priming
electrical bilge pump by dropping the intake hose into the
distribution box through the vent pipe. Removal of the ponded water
in this way did not cause a significant rise in the tensiometer
reading, indicating that very little water was seeping through the
soil layers below the bed. About 1.5 inches depth of water remained
in the distribution box. The residual water in the rest of the bed
was unknown. While approximately 500 gallons of clean water was
being added through a garden hose into the vent pipe on the
distribution box, 15 gallons (pounds) of standard grade (ca. 52%)
hydrogen peroxide was siphoned in. Frothing could be seen and heard
in the distribution box and in the stand-pipes. Within a few hours
the tensiometer readings began to fall, indicating that the
clogged/crusted layers of the soil had been perforated and water
was moving into lower soil horizons underneath the bed. The fresh
water actually drained from parts of the bed before effluent began
flowing into the distribution box again after the tank refilled. As
effluent began discharging into the bed again, the tensiometer fell
after 7 days from an initial reading of 376 cm (before treatment)
to 240 mm of mercury, the value for saturated flow in this type of
soil. In time, the tensiometer rose again gradually to 280 mm after
3 months, when measurements were discontinued; some water was
ponding in the distribution box, but the ends of the distribution
system were still dry, where the standpipes had been inserted. The
ends of the bed were still dry 12 months after treatment. The
distribution box was not full, and no effluent was surfacing.
EXAMPLE 4
In another badly underdimensioned system on glacial till, effluent
was spilling out over the top of a vent pipe at the lowest end of
the disposal bed and forming a large surface pond in a hollow at
that end of the system. A pit was dug and a tensiometer inserted in
soil beneath the failed seepage bed about 15 feet from the vent
pipe. The pit was closed, the 650 gallon septic tank emptied by a
commercial pumper and the effluent from the bed pumped out onto a
nearby pasture. The intake hose to the gasoline pump used was
inserted into the vent pipe and later in a perforated 10-foot stand
pipe inserted with a post hole digger and soil auger into the bed
on the other side from the tensiometer. After pumping, the bed was
filled with 20 gallons of standard grade 52% hydrogen peroxide,
diluted with 500-600 gallons of water. Almost immediately the
tensiometer reading began to fall from its initial value of 378 mm
of mercury. After 3 days, the lowest value of 273 mm was recorded.
In the following days and weeks the value rose gradually but
remained quite steady at 280-282 mm. Thus, breakthrough of
clogged/crusted layers causing failure of the system had been
achieved. Because of heavy overloading of the system (750
gallons/day water use by a family of 16), water soon began to pond
in the system again, as viewed in the standpipe. However, no water
had resurfaced 3.5 months later, when the system was replaced by a
larger tank and a sand filter.
As pointed out hereinbefore, the concentration and amount of
hydrogen peroxide used is not critical. In all events, the
concentration will be commensurate with safety in use, depending
upon whether a professional in the business or a homeowner will
handle the chemical, and with economy -- the amounts will be
sufficient to properly "open-up" the seepage bed and will obviously
be dependent upon the size of the particular installation being
treated. Repeated sequential applications can, of course, be made
in the event a single application is insufficient to re-establish
drainage in a bed. The hydrogen peroxide is convenient to use in
concentrations from about 25% to about 65%. Concentrations lower
than 25% can be readily used but are less economical particularly
where shipping costs are involved. Concentrations higher than about
65% and up to 100% can be used but such higher concentrations
present substantial safety hazards in shipment and use. In most
cases, in the treatment of seepage beds, appropriate on-site
dilutions should be made to substantially reduce the actual
concentration of the hydrogen peroxide in the bed. Dilutions to a
peroxide concentration in the bed of from about 1 to about 5% are
eminently suitable.
Where hydrogen peroxide is to be used for the prophylactic
treatment of seepage beds, as pointed out above, it may be
desirable to utilize a stabilized form of the peroxide, i.e. where
the peroxide solution has been stabilized against catalytic
decomposition by, for example, borates or organic stabilizers. Such
a stabilized composition is much less likely to exhibit localized
foaming which is evidence of catalytic decomposition and which
dissipates the available oxygen in the peroxide without optimum
beneficial effects. Stabilized hydrogen peroxide solution are well
known in the industry and may contain, as stabilizing agents,
methanol, ethanol, glycerol, barbituric acid, boric acid, etc.
As pointed out above, other inorganic and organic peroxides such as
sodium peroxide, barium peroxide, peroxyalkanoic acids, and alkyl
hydroperoxides can be used in the place of hydrogen peroxide, as
can other oxidizing agents such as oxygen or ozone, and even
chlorine or oxychlorides. However, use of such materials are
militated against by reason of their expense, difficulties in
application and highly undesirable side effects. In circumstances
where some or all of such disadvantages can be tolerated such
oxidizing agents can be used instead of hydrogen peroxide.
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